How to Make Plaster Molds for Slip Casting
Molds provided an easy way to manufacture many copies of an object. Molding ceramic in particular is a quick shortcut for thrifty artists. Historically, potters used molds with ceramics to create whole objects or decals that they could add on to a hand-cast piece. Creating a molded ceramic piece requires the use of slip, a liquid sludge of clay and water that hardens over time and shrinks away from the walls of the mold. You always want to make your mold larger than the end piece you want, as all pottery shrinks, though the actual shrinkage amount varies depending on the individual clay.
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Things You'll Need
- Prototype
- Pottery plaster
- Bucket
- Sink
- Gloves
- Dust mask
- Newspaper
- Talc powder
Instructions
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1
Lay newspaper over a workspace and place your prototype in the center. Put on a dust mask and gloves. Although pottery plaster is non-toxic, you are better off safe than sorry. Dust your prototype with talc powder.
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2
Pour pottery plaster into a bucket, stop when it is half full. Pottery plaster is a white powder that you can find in large quantities at any craft store. It reacts chemically with water to form a sludge that eventually hardens into a clay-like material that absorbs water.
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3
Place the bucket in a sink and begin filling it with water. Mix the water and plaster together with your gloved hands. Stop the flow of water when the plaster reaches a consistency of mud. Most manufacturers advise mixing seven parts of water to 10 parts of plaster, but you should really do it to the touch.
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4
Scoop up handfuls of the plaster and dab it over your prototype. Work quickly, as the plaster will begin to harden and become crumbly in a few minutes. Once it is crumbly it will not adequately take the shape of the prototype you put it on.
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5
Mix up some more plaster after half an hour if the shell around your prototype is too thin. The shell needs to be at least 1 inch thick on all sides. Dab the newly mixed plaster on top of the shell for additional structural support.
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6
Allow the piece to harden for 24 hours. Ideally, you should wait two weeks for the piece to be fully bone dry, but you can use it after a full day.
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7
Flip the mold over and peel the stuck newspaper away. Gently pry the prototype out of the mold.
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Tips & Warnings
Oil clay makes a great, reusable substance for a prototype if you wish to sculpt your own. It also peels fairly easily off of hardened plaster, although the prototype will be ruined in the process.
References
- Photo Credit Head of plaster image by Pontus Edenberg from Fotolia.com
